A power management system is widely used to save power consumption in a personal computer system. Advanced Configuration and Power Management Interface (ACPI), which was published by Intel, Microsoft and Toshiba in Dec. 22, 1996, is a specification defining standard interfaces for hardware configuration and power management of a power-saving system. According to the ACPI specification, the function of power management is integrated into the operation system to increase the efficiency of power management and the processing speed of the computer system.
According to the ACPI specification, the power management of the computer system is classified into six modes including S0 (a normal mode), S1˜S4 (suspended modes) and S5 (a power off mode) from low to high. Each of these different suspended modes S1˜S4 allows for different level of power saving and usage. A computer system in the S1 mode simply shuts down the hard drives and the monitor, but leaves everything else running normally. S2 mode offers slightly greater power saving than the S1 mode. A computer system in the S2 mode not only shuts down the monitor and hard drives, but also interrupts power to be supplied to the CPU and its cache. A computer system in the S3 mode shuts down almost everything except for the RAM and the power management controller. The S3 mode is also referred as a “suspend to RAM” mode to listen for a wake-up action. When the computer system comes into the S3 mode, the ACPI allows the RAM to store the last operation of the computer system. When the computer system is turned back on from the S3 mode, the computer system is quickly restored to the last operation based on the data stored in the RAM without normal booting. S4 mode is known as a hibernation mode in which the entire computer system is stopped and all of the system modes and contexts are stored to disk selected by the BIOS. The S4 mode is also referred as a “suspend to disk” mode.
On the other hand, the computer system principally comprises a host computer, a monitor and other peripheral devices. The monitor may be a cathode array tube (CRT) monitor or a liquid crystal display (LCD). Recently, the LCD monitors are becoming popular. The host computer transmits video signals to the monitor via signal lines. The peripheral devices are also electrically connected to the host computer. Generally, the host computer and the monitor are distant from each other. For example, the monitor is placed on a table, whereas the host computer is placed under the table. As such, when the host computer is to be started, the user needs to bend down to press the power button, which is not user-friendly. The common human-machine interfaces for the computer system include the monitor, the mouse, the keyboard, and the front panel of the host computer (which is used to turn on/off the host computer, draw out/insert disks or swap IEEE 1394 interface and USB devices, etc). However, among these the human-machine interfaces, the monitor, the mouse and the keyboard are frequently manipulated by a computer user when a computer system is used.
U.S. Patent Application Publication 2003/0107566, which is published in Jun. 12, 2003, describes the use of an external USB device such as a keyboard or a mouse to control the turning on/off state of the host computer. This technology provides a monitor having a USB hub in connection with external USB devices. In addition, a digital video interactive (DVI) cable is employed to connect the monitor with the power output port, the graphic card and the USB port of the host computer so as to transmit video signals from the host computer to the monitor for display. In the S3 mode of the power management system of the host computer, by operating the input/output device, for example, a USB keyboard or a mouse connected to the USB hub of the monitor, a USB controller inside the monitor will transmit a wake-up signal to the host computer via the USB cable to wake up the host computer from the power saving mode to the normal mode.
According to the above technology, the host computer can be woken up by employing a keyboard or a mouse. However, the external device should be connected to a monitor having a USB hub. Since the ordinary LCD monitor has no USB hub to connect the external USB device, this LCD monitor should be specifically designed. For example, an internal USB hub is provided in the LCD monitor as a connection medium of the external device. The fabrication cost of this LCD monitor having an internal USB hub is relatively high. After a triggering signal is asserted from the external device, the USB controller in the monitor will transmit a wake-up signal to the host computer to wake up the host computer from the suspended mode when the USB controller detects an input signal from the input/output device via the USB hub. However, such means of waking up the host computer by signal transmissions from the USB device to the LCD monitor and then from the LCD monitor to the host computer is inefficient. Furthermore, two power supply apparatuses are required by the LCD monitor to generate driving power for the USB controller and the USB hub, which is not cost effective.